Gas turbine engines are used to power aircraft, watercraft, power generators, and the like. Gas turbine engines typically include a compressor, a combustor, and a turbine. The compressor compresses air drawn into the engine and delivers high pressure air to the combustor. In the combustor, fuel is mixed with the high pressure air and is ignited. Products of the combustion reaction in the combustor are directed into the turbine where work is extracted to drive the compressor and, sometimes, an output shaft. Left-over products of the combustion are exhausted out of the turbine.
Compressors and turbines typically include alternating stages of static vane assemblies and rotating wheel assemblies. The rotating wheel assemblies include disks carrying blades around their outer edges. When the rotating wheel assemblies turn, tips of the blades move along blade tracks included in shrouds that are arranged around the rotating wheel assemblies.
During operation, the tips of the blades included in the rotating wheel assemblies typically move inwardly and outwardly relative to a centerline of the engine due to changes in centrifugal force and temperatures experienced by the blades. Because of this movement inwardly and outwardly relative to the centerline, the case around the blades is sometimes designed to allow clearance between the blade tips and the blade tracks. This clearance may allow combustion products to pass over the blades without pushing the blades, thereby contributing to lost performance within a gas turbine engine.